Insulin resistance and beta cell failure play key roles in the pathogenesis of type 2 diabetes. The goal of this application is to understand the pathophysiology of these metabolic abnormalities by introducing mutations into genes important for insulin action and/or beta cell function in mice. Over the last five years, the PI's laboratory has developed several transgenic and knockout mice with mutations in the insulin receptor signaling pathway. These murine models have elucidated the metabolic role of insulin receptors in the whole animal and in insulin-dependent tissues, as well as their role in embryonic growth. Moreover, mice with combined mutations of the insulin receptor and its substrate IRS-1 have elucidated in vivo signaling mechanisms and genetic interactions leading to type 2 diabetes. The PI proposes to continue to characterize gene function using genetically engineered mice, expanding the repertoire of available mutations and completing detailed metabolic studies of existing strains. There are four aims in this proposal. In Aim 1, the PI proposes to address the pathophysiology of insulin resistance in the adult mouse by generating a model of inducible gene knockout using a novel strategy based on the Cre-lox binary mutagenesis system, and by characterizing mice with liver-restricted expression of insulin receptors. Studies described in Aim2 will address the role of IRS-1 and IRS-2, the two main substrates of insulin and IGF-1 receptor signaling, in insulin action. To this end, the PI will characterize mice with combined null mutations of insulin and IGF-1 receptor, IRS-1 and IRS-2, and generate an insulin receptor "knock-in" mouse with a single amino acid substitution in the Juxtamembrane domain (Y972F) to dissect the specificity of IRS-1 vs. IRS-2 signaling. In Aim 3, crosses among mice with mutations of insulin receptor, IGF-1 receptor, insulin receptor-related receptor as well as IRS-1 and IRS-2 will be used to investigate the signaling mechanism(s) required for beta cell growth and insulin secretion. Aim 4 is based on preliminary studies in which the PI identified murine quantitative trait loci (QTLs) that affect plasma insulin level by interacting with a null mutation of the insulin receptor gene. Additional mapping of the QTLs is proposed as a preliminary to positional cloning of the relevant genes.